Abstract : The paper represents an attempt to derive from the literature on small groups some notion of the variables underlying the effectiveness of groups in resolving complex and difficult problems. Major emphasis has been placed on studies published between 1955 and 1962. Five sections comprise the body of the paper. The first three deal with background material, the last two with group structure and process per se. The role of cognitive variables in group performance is considered in Section I; the problem of group code orientations is taken up in Section II. Group motivation and behavior under pressure are discussed in Section III. Finally, in Sections IV and V, these variables are considered from the standpoint of their interactions with such group process variables as code formation, social power, information flow, and conformity, and with such structural variables as clique hierarchies, cohesion, formal status and leadership, and communication networks.